Document: BRI-3-34-54

Symbiotic N-fixer responses to simulated global change in a California grassland.

THOMAS, B.D.* ^1,2

Stanford University, Stanford, CA 94305 USA ¹
Carnegie Institution of Washington, Stanford, CA USA ²

Abstract:
Factors that regulate symbiotic nitrogen fixing plants may indirectly control nitrogen limitation in numerous terrestrial ecosystems. I quantified the responses of Vicia sativa, a common California grassland legume, to the manipulation of atmospheric CO₂ concentration, temperature, precipitation, and nitrogen deposition in an annual grassland at Jasper Ridge Biological Preserve near Stanford, CA. In this study, the primary impacts of simulated global change on Vicia were mediated by plant community dynamics and trophic interactions. The heating treatment had a positive impact on Vicia biomass (Kruskal-Wallis ANOVA, (P<0.05) and reproductive output (P<.005). Nitrogen additions had a negative impact on both biomass (P<0.001) and reproductive output (P<.001). The nitrogen effect was in agreement with current understanding of N-fixer competitive ability under high nitrogen availability, corroborated by clear increases in community aboveground biomass with fertilization. The heating effect was due in part to the acceleration of dominant grass phenology (which favored the phenologically indeterminate Vicia) and to changes in herbivory: Heating had negative impacts on population sizes of common herbivorous mollusks (P<0.05) and consequently on Vicia foliar herbivory losses (P<0.001).

Keywords: symbiotic nitrogen fixation, global change, herbivory

This abstract is being presented at: 3:30 PM in session:
Poster Session #17: Vegetative Analysis.